McQuay AGZ026BS, Installation, Operation And Maintenance Manual

Page: 17 / 106

IOMM AGZ-5 AGZ 026B through 130B 17
Water Connections
Bring water piping to the evaporator through the side between the vertical supports.
Provide taps for the connection of pressure gauges and thermometers in the inlet and
outlet lines. Check the inlet and outlet labels on the unit against the certified drawings
supplied on the job and be sure the water piping is hooked up correctly. Contact the
McQuay sales office if any discrepancies exist.
System Water Volume Considerations
All chillers need adequate time to recognize a load change, respond to the change and
stabilize without short cycling the compressor. The water volume in the system and the
size of the piping loop is a critical consideration. Good engineering practice is to have
a minimum water volume of four times the flow rate (GPM) for comfort cooling
applications. For process applications where the load can change quickly, contact the
local McQuay sales office for recommendations. A water storage tank (provided by
others) may be required to increase the system water volume in some systems.
Since there are many other factors that can influence performance, systems can
successfully operate below these suggestions. However, as the water volume decreases
below these suggestions, the possibility of problems increases. We believe that these
guidelines should be an industry standard and not just recommendations from McQuay.
Variable Speed Pumping
Variable water flow involves reducing the water flow through the evaporator as the
load decreases. McQuay chillers are designed for this duty provided that the rate of
change in water flow is not greater than 10 percent of the change per minute.
The water flow through the vessel must remain between the minimum and maximum
values listed on page 22. If flow drops below the minimum allowable, large reductions
in heat transfer can occur. If the flow exceeds the maximum rate, excessive pressure
drop and tube erosion can occur.
Glycol Solutions
The use of a glycol/water mixture in the evaporator to prevent freezing will reduce
system capacity and efficiency, as well as increase pressure drop. The system capacity,
required glycol solution flow rate, and pressure drop with glycol may be calculated
using the following formulas and tables.
1. Capacity – Multiply the capacity based on water by the Capacity correction factor
from Table 7 through Table 10.
2. Flow – Multiply the water evaporator flow by the Flow correction factor from
Table 7 through Table 10 to determine the increased evaporator flow due to glycol.
If the flow is unknown, it can be calculated from the following equation:
)
) ( 24
(gpm) Flow Glycol Factor Correction Flow
T Delta
glycol Capacity Tons
×
−
×
=
For Metric Applications – Use the following equation for metric applications:
Factor Correction Flow
T Delta
Capacity kW
×
− ×
=
18 . 4
(l/s) Flow Glycol
3. Pressure drop -- Multiply the water pressure drop from page 22 by Pressure Drop
correction factor from Table 7 through Table 10. High concentrations of propylene
glycol at low temperatures may cause unacceptably high pressure drops.
4. Power -- Multiply the water system power by Power correction factor from Table 7
through Table 10.